This invention relates to a vehicle heating and air conditioning system in which a driver-manipulated temperature selector is physically coupled to a temperature control device for adjusting the discharge air temperature of the system, where the temperature selector is operable in a selected one of two modes.
Manually regulated vehicle heating and air conditioning systems include an operator interface for enabling or disabling air conditioning, and for selecting airflow mode (i.e., panel, defrost, etc.), blower speed, and discharge air temperature. When air conditioning is enabled, a refrigerant compressor is activated and then capacity controlled based on a system temperature or pressure to maintain the evaporator temperature a few degrees above the freezing point of water to provide maximum cooling and dehumidification while preventing evaporator icing. The discharge air temperature is selected by positioning a temperature control lever or knob, which is often physically coupled to a temperature control door that directs all or a portion of the air exiting the evaporator through a heater core coupled to the engine coolant circulation system. In typical operation in warm ambient conditions, the driver will enable air conditioning, and set the blower speed to high and the temperature selector to full cold. As the vehicle cabin cools down, the driver usually lowers the blower speed and adjusts the temperature selector until a desired combination of discharge air flow and temperature is achieved. In this scenario, the compressor control remains essentially unchanged, and a portion of the air exiting the evaporator is re-heated by the heater core to achieve the desired air discharge temperature.
It has been recognized that the efficiency of the above-described control can be improved by regulating the capacity of the compressor as the temperature selector is moved away from the full cold setting. In this way, the evaporator temperature is allowed to increase above the full cold setting, and the need for re-heating to achieve the desired air discharge temperature is reduced. For example, the U.S. Pat. No. 4,383,574 discloses a control wherein movement of the temperature selector in the cold-to-medium portion of the temperature control range changes the capacity of the refrigerant compressor while an air mixing device is maintained in the full-cold position, and movement of the temperature selector in the medium-to-hot portion of the temperature control range changes the position of the air mixing device to heat the discharge air.
While a system like that described in the aforementioned U.S. Pat. No. 4,383,574 can achieve improved system efficiency when air conditioning is enabled by lowering the compressor input power requirement, it requires an alteration of the usual coupling between the temperature selector and the temperature control door that prohibits normal operation of the system, which is required for maximum dehumidification. It also creates an undesired temperature control non-linearity when air conditioning is disabled, since movement of the temperature selector in the cold-to-medium portion of the temperature control range will produce no change in the discharge air temperature. Accordingly, what is needed is a heating and air conditioning system including manually adjusted temperature selector that is capable of being selectively operated in either a normal mode for maximum dehumidification or a high fuel efficiency mode for reducing energy consumption at a somewhat higher cabin humidity level, where linearity between selector movement and discharge temperature adjustment is preserved regardless of the selected mode.
The present invention is directed to an improved vehicle heating and air conditioning system including a driver-manipulated temperature selector that is physically coupled to a discharge temperature control mechanism, wherein the selector is operable in a normal mode in which movement of the selector away from a full cold setting produces a corresponding movement of the temperature control mechanism that increases the discharge air temperature by re-heating or a high fuel efficiency mode in which movement of the selector away from the full cold setting allows the temperature control mechanism to remain in a full cold position for a limited range of selector movement while the discharge air temperature is increased by capacity reduction of the refrigerant compressor. In the preferred embodiment, the temperature selector is in the form of a rotary knob that is axially shiftable to change modes when the selector is positioned at the full cold setting and spring-biased so that the normal mode is established as the default mode.